More than brother does not necessary mean Lover.
I mean they have been all on their own, so he tried to be her brother, her protector, her father and mother all at once.
Maybe she only meant, that he was her "everything" because he took care of her instead of their dead parents and there was no adult around they could trust. So she could no longer imaging a future without him, because he was her whole world.
Ok then go to ur fam member and tell them you have feelings for them that are more than father/mother/brother/sister-ly like that is definitely not what was coming across in the manga
K.O.
Is no one gonna talk about how his sister his SISTER had feelings for him??????